1. Field of the Invention
The present invention relates to silicone rubber compositions whose cured product is improved in flex fatigue resistance and extension fatigue resistance, a process for the production thereof, and their cured product.
2. Description of Prior Art
Since silicone rubbers are excellent, for example, in electrical resistance, heat resistance, cold resistance, weather resistance, permanent compression set, and rubberiness and are non-toxic, they are used in various fields, for example, for electrical and electric components, various business and office machines, automobiles, airplanes, materials for foods, medical materials, and leisure goods. The application of silicone rubbers is not limited to these static uses and includes many dynamic uses, for example, for rubber contacts of electric calculators and push-button phones, keyboards, uniform rate joint cover boots of automobiles, diaphragms, and medical pump tubings.
However, conventionally known silicone rubbers are not necessarily satisfactory in flex fatigue resistance and extension fatigue resistance particularly in dynamic uses and the flex fatigue resistance and extension fatigue resistance thereof are desired to be improved.
To meet that, also in silicone rubbers, techniques are used that improve the dynamic fatigue resistances of common synthetic rubbers, such as, uniform crosslinking, lowering of crosslink density, lowering of modulus, decreasing of the load of fillers, uniform dispersion of fillers, and elimination of coarse particles of fillers. However, even when these techniques are used, the flex fatigue resistance and extension fatigue resistance of silicone robbers are at the level at most of 1,000,000 times by the most common de Mattia fatigue test method and satisfactory flex fatigue resistance and extension fatigue resistance have not yet been attained in their dynamic uses.